Rapid-fire firearms came into common use at the beginning of this century. The firearms used recoil or gas siphoned from the discharged round to do the work of cycling the loading mechanism of the firearm. Initially, these firearms were heavy, crew-serviced firearms such as Maxim and Browning belt-fed machineguns. The crew-serviced machineguns were soon followed by lighter, individual-use firearms, such as the Thompson sub-machinegun. In the case of shoulder-fired firearms, operators noticed significant “climb” when discharging the firearm. In response, devices were developed to attach to the muzzle of a firearm to compensate for climb. The nomenclature for this family of devices is muzzle compensators, or more commonly muzzle brakes.
An early muzzle brake was the Cutts Compensator, which is described in U.S. Pat. No. 2,165,457. The Cutts device consisted of a tubular muzzle attachment that had several rows of horizontal slots cut across its top surface and a partially occluded end cap on its front surface. As the high-pressure gases, behind the discharged bullet, exited the bore of the firearm, they would seek the path of least resistance, and flow through the compensator's rows of slots. The flow created a downward impulse at the muzzle of the firearm. The venting of gases was thus used to do constructive work. The Cutts device represented a limited improvement in muzzle control over a “naked” muzzle.
The second half of the twentieth century brought the advent of the assault rifle. The sub-machinegun's high magazine capacity and automatic fire capability were mated with the high-powered cartridges of the rifle. The combination proved to be a very powerful and flexible tool for the operator. The higher power ammunition of this family of firearms, however, makes them more difficult to control than the earlier machineguns during rapid or automatic fire. The advent of the machine pistol also added to the problem of lighter weapons mated with higher power cartridges.
Muzzle climb, in the form of both lateral deviation and vertical climb, became a significant contribution to wasted ammunition expenditure because assault rifles and machine pistols climb off target even more quickly than earlier designs. When an operator discharges a firearm, captured high pressure gas, located behind the projectile, force the projectile along the bore of the firearm. The force generated by the expanding gas causes the projectile to accelerate until it exits the bore, and the gas dissipates in the open air. As the projectile physically exits the bore of the firearm, a point of equilibrium is established between the momentum of the forward moving projectile with expanding gas behind it, and the rearward momentum of the firearm itself, due to opposite but equal momentum within the system. The rearward impulse is known as recoil.
If the firearm is in a relatively balanced testing cradle, the recoil impulse will cause the firearm to move rearward in a fairly straight line. However, if a human operator is the basis of the firing platform, the original straight-line recoil impulse will be translated into distortions of the firing platform due to human body mechanics. In an offhand shooting position, the feet and legs represent the fixed end of a pendulum with a center of mass commonly two to three inches behind the navel. A momentary force is applied at the opposite end of the system causing a complex set of angular momentums. Due to these factors, the firearm muzzle is seen to climb vertically and also rotate around a vertical axis.
When the firearm operator is executing slow, aimed fire, the above recoil-related factors create a minimal impact upon the effectiveness of the operator, because the operator has the time to “reset” into the original firing position between discharges. However, as the firearm operator increases the number of recoil impulses per unit of time, the effectiveness of the operator correction diminishes.
Multiple recoil impulses in rapid succession effectively become a continuous torque on the system. The coincidence between the original point of aim and point of impact of subsequent rounds decreases as the number of recoil impulses increases. The greater number of rounds in the burst fired, the greater the variance between the point of aim and subsequent points of impact. At close distances of fifteen meters or less, muzzle climb may not be a significant problem for the firearm operator. However, at greater distance, this radical muzzle climb will greatly diminish the effectiveness of the operator.
Variations on the Cutts design, such as the M-16A2 solid bottom birdcage and the AK-47 wedge, were developed in an effort to solve the problem. However, none contributed significantly to the field. In fact, nearly half a century passed before the next significant development, which is described in U.S. Pat. No. 4,635,528 to McQueen. Like the Cutts device, the McQueen design consisted of a round tubular muzzle attachment with slots cut across the top surface, and a partially occluded front end cap. However, unlike the Cutts device, the front-end cap on the McQueen design was threaded, and adjustable for inward and outward movement within the body of the stabilizer. Though many existing firearm muzzle compensators could be adjusted for right-left horizontal/lateral roll, the McQueen design was adjustable for two axes with its introduction of the adjustable high-pressure gas flow regulator into the system. Although the flow of gas could be adjusted, the adjustment was relatively course. Thus, the McQueen device could not provide adequately fine adjustment for the magnitude of the corrective force. In addition, the McQueen design was limited to rifles utilizing cartridges of up to medium power. The design included a single-stage expansion chamber. When used with high power cartridges, a single-stage expansion unit can break apart or even detach from the end of the muzzle and become a projectile.
A related patent, U.S. Pat. No. 4,813,333 to Garris et al., addressed what may be considered “marketing” issues. Designers decreased the body length of the McQueen device to meet dimensional specifications demanded by customers. This modification created higher stresses on the anterior portions of the device. To compensate, the designers opened the angled gas vent and used holes instead of slots for the forward vertical vent. In this configuration, the device functioned, but did so less effectively than the McQueen design, and was restricted to use with low to medium powered cartridges.
None of the known muzzle stabilizers provide adequately fine adjustability of the magnitude of corrective force. In addition, the known devices fail to provide adequate stability for firearms using high-power rounds. Therefore, a need exists for a dually adjustable muzzle stabilizer with improved fineness of adjustability to provide adequate stability during rapid firing, even when high-power cartridges are used.